I like the concept of critical successes and the skillful recoveries. I agree there needs to be mechanics to keep the players involved. Have you thought about how to include the use of action points and/or healing surges into the system? Those are resources that the players control that renew and seem to lend themselves to encounters.
A suggestion for critical successes, instead of a natural 20 or +10, try +5 over the states DC. Another simple option is to allow skillful recovery as an option all the time but it adds another failure on a miss. Or a failed recovery imposes a -2 penalty on the next check.